The art is cognizant of the use of enclosed structures for drying wet or damp materials, such as lumber, grain, and tobacco. Piver, U.S. Pat. No. 487,965, shows such a structure or "house" for drying lumber in which a furnace is used to supply heat to facilitate the drying process. Thomason, U.S. Pat. No. 3,412,728, Mayo, U.S. Pat. No. 2,529,621, and Huang, U.S. Pat. No. 3,866,334, all show drying houses or kilns that employ solar radiation as a source for at least part of the heat used in the dryer. Mayo and Huang provide for furnaces that are simply aided by a contribution from solar energy. Thomason and Mayo provide for the introduction from the outside of fresh air into the system and the venting of inside air that has become excessively humid.
When an enclosed structure is used for drying large amounts of material or material such as lumber that comes in large pieces, convenient, unobstructed access to the interior of the structure is desirable. Piver and Huang show wheeled vehicles or carts to carry the material to be dried, together with doors in the end or side walls of their dryers especially adapted to admit them. Lager shows a miniature greenhouse that is essentially a rectangular glass box with a slant roof. The roof opens upwardly, being hinged at its back edge. Access is then had from above.
The prior art is cognizant of the need to insulate heated drying houses and the like from the cooler, ambient atmosphere. Thus, Mayo shows an insulative layer in the roof of a drying house. Gahler, U.S. Pat. No. 3,791,076, shows a double layer, plastic greenhouse wall constructed of a flexible, light-admitting sheet material. The double sheets of plastic are inflated to space their central portions apart and provide an insulative double glazing.
In maintaining an elevated interior temperature for a drying house or other device for drying wet materials, it is desirable to avoid wasting the heat of humid interior air at the same time that is necessary to provide some sort of venting or dehumidification system to remove moisture from the interior of the drying house. Mayo shows partial recycling of the heated air of the drying house disclosed, presumably until the air is no longer efficient as a drying medium. Furthermore, a heat exchange system is provided wherein exhausting air is allowed to warm a heat sink that in turn warms incoming air.
It is also known to use conventional, electrically powered dehumidification systems to remove humidity from the air of a dryer. For a discussion of such dryers, see "Experimental Solar-dehumidifier Kiln for Drying Lumber," Peter Y. S. Chen, et al., Forest Products Journal 32(9): 35-41 (1982). The cost of operating such a dehumidification system can be high, however, and must be weighed against the cost of simply venting humid air and heating new, dry air drawn from outside the system. In addition, such electrical dehumidification systems generally must employ fairly complicated machinery. Such machinery is subject to breakdown, especially in the often corrosive atmosphere of a drying device loaded with green lumber. Furthermore, if the dehumidifier utilizes a conventional two coil refrigeration mechanism to condense out water from the air, a choice must be made between locating the radiating coil of the dehumidifier outside the drying chamber, in the cooler, surrounding atmosphere, or inside, where heat will not be lost from the dryer but the efficiency of the dehumidifier will be reduced and the coil may be subject to corrosive conditions.
The prior art is not cognizant of a unified system adapted to simultaneously dehumidify the air from within a solar heated drying device and provide for improved thermal insulation of the interior of the device from the cooler ambient atmosphere. Furthermore, the art is not cognizant of such a system that also provides nearly unrestricted access to the interior of the drying device.